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Fiberglass bats in basement walls

Rock Rau's picture

I am finishing my basement and have finished building the stud walls. I am planning to use faceless fiberglass batts in the exterior walls. My house was built in 1999 with poured concrete walls and floor with a 1 1/2" gap between the walls and the floor(floating slab?). So between the 1 1/2" gap between floor and walls and plus a 4" drain pipe  hanging on the walls the distance between the  stud wall and the concrete wall is at least 2",where the pipe is 5" and in another place,  a foot. So my question is what will keep the faceless batts from falling into the cavity between the stud wall and the concreate foundation wall??? Or am I concerned over nothing? My main resorces are FineHomebuilding and a book published by Taunton's " Remodeling a Basement " by Roger German.

Any help or information will be greatly appreciated, Rock.

You're right to be concerned (post #215033, reply #1 of 20)

You're right to be concerned beause the batts will fall without some sort of support. You can staple rows of string across but that's probably going to be tough or you could wrap the string around the studs but that be will take a lot of time. You could installed faced insulation then slash the paper so it isn't a vapor barrier but you have to do so carefully so the fiberglass doesn't fall off. Or, maybe glue foamboard to the back? Tough job.

Florida Licensed Building Contractor, 45 years experience in commercial remodeling, new homes, home remodeling and repairs and all types building maintenance.

There is an inexpensive (post #215033, reply #2 of 20)

There is an inexpensive webbing material that comes on rolls.  It's like the webbing straps that come on backpacks.  I bought some at Lowes.  Cuts with a scissors and you can staple or screw it to the studs to keep the batts from falling.  I used it to secure fiberglass between floor joists in a basement/crawlspace ceiling.

You're right! I had a brain (post #215033, reply #3 of 20)

You're right! I had a brain fart as we just used the netting on a job several months ago. good stuff.

Florida Licensed Building Contractor, 45 years experience in commercial remodeling, new homes, home remodeling and repairs and all types building maintenance.

Dunno about you guys, but if (post #215033, reply #4 of 20)

Dunno about you guys, but if I had bats flying around loose in my basement I'd call an exterminator.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Can someone please give me a (post #215033, reply #5 of 20)

Can someone please give me a company or a vendor for the netting? It seems Lowes and my local lumber yard have never heard of the prduct. I guess it is not used in my area. I need to shop online. Thanks!

I found the product on Lowe's (post #215033, reply #6 of 20)

I found the product on Lowe's Web site.  It's called Duct Support Webbing.  The manufacturer is Cambridge Resources.  You'll see the picture of the product being used to hang some ductwork.  In Lowes it's located in the same aisle as the duct work.

You might want to look at (post #215033, reply #7 of 20)

You might want to look at mineral wool batts. They are much stiffer that fiberglass, and do not require straps to hold them in place.  Price is a little more expensive than fiberglass, but you will save the cost of strapping the wall.  They are better at insulating as well.

If you are going with fiberglass, running cord every 6", wrapping around the studs may be easier than trying to staple straps to the back side of the studs in a narrow gap.

Roxul (post #215033, reply #18 of 20)

Well, you guys have really helped me out!   I have looked into Roxul and it seems to be the perfect product for my application!

Can I use Roxul for a fire stop instead of 2X ?

The cord method (post #215033, reply #8 of 20)

The cord method sounds easier. Where can i get it? Also does mineral wool support mold growth? The whole purpose of me using faceless bats is to advoid mold.

Roxul Mineral Wool is (post #215033, reply #9 of 20)

Roxul Mineral Wool is available at Lowes.  I had a product pamphlet...I think it said it's not bothered by water.....probably won't support mold growth. 

Where is the house located? (post #215033, reply #10 of 20)

Where is the house located?

Just about any twine will (post #215033, reply #11 of 20)

Just about any twine will do.   The cheap blue/white polypropeline twine used for packaging is suitable; The stuff at the big box stores used for tying stuff to car roofs and such.  Mason line is readily available at reasonable cost.

Mineral wool is made fom rock and recycled steel slag.  It will not support mold or mildew by itself.

Location (post #215033, reply #12 of 20)

Home is SE PA, Bucks Co.

Mineral wool is far better (post #215033, reply #13 of 20)

Mineral wool is far better suited to a basement environment. You can soak mineral wool in water and it retains all R-value when it dries out. Fiberglass loses its R value once wet 

I need to take a closer look (post #215033, reply #16 of 20)

I need to take a closer look at  mineral wool! Sounds like a better product for my application.

Thanks Guys! I'll keep you posted.

FWIW (post #215033, reply #14 of 20)

FWIW, a FHB article from several years ago strongly suggests using foam board for insulating basements for several reasons, including the capacity to block moisture from entering the conditioned space. 

Sort of like what is displayed in the other post about a NE basement. 

Good luck. 

I decided not to use the foam (post #215033, reply #15 of 20)

I decided not to use the foam board since three of the exterior walls have a 4" drain attached to them. I just finished building the walls and it occured to me that the bats could fall out. Hind sight is 20/20!

Hindsight..... (post #215033, reply #17 of 20)

Moisturre control is your friend in a basement. Are you going to put a vapor barrier up once the walls are insulated?  Perhaps even put down a layer of foam on the outside of the wall before the drywall?

I think Rockwool is going to be far better than FG is your appication. 

I had some attics spray foamed last year. To jump voids from stud to stud, they stapled plastic sheet (similar to cheap dropcloths)  on the outside of the studs and then foamed against the sheet plastic. Of coure, this presumes you have the clearance behind the studs to run and staple or tape the plastic. The closed cell spray foam was surprisingly inexpensive and very effective. 

Good luck. 

Vapor barrier (post #215033, reply #19 of 20)

According to " Remodeling A Basement " by Roger German(Taunton's 2010) pg. 99 that research compiled by the Building Science Consortium presents a new consensus on the best way to keep your basement warm while avoiding mold and mildew problems and unhealthy airquality.  " It is better to omit the vapor barrier altogether".

But I am still hearing that poeple are using a vapor barrier.

So when the time comes (a month or two) ,unless I learn different I am not going to install a vapor barrier....?

Yet... (post #215033, reply #20 of 20)

There is a different article in FHB about insulating basements that strongly counsels sheet foam. 

Good luck.